In a typical inkjet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the recording element. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent. The solvent, or carrier liquid, typically is made up of water, an organic material such as a monohydric alcohol, a polyhydric alcohol, or mixtures thereof.
Inkjet image recording elements have been designed in recent years to achieve photographic quality images when ink is applied to them from an inkjet printer. An inkjet recording element typically comprises a support having on at least one surface thereof at least one ink-receiving layer. The ink-receiving layer is typically either a porous layer that imbibes the ink via capillary action, or a polymer layer that swells to absorb the ink. Swellable hydrophilic polymer layers take an undesirably long time to dry compared to porous ink-receiving layers.
Porous ink-receiving layers are usually composed of inorganic or organic particles bonded together by a binder. The amount of particles in this type of coating is often far above the critical particle volume concentration (CPVC), which results in high porosity in the coating. During the inkjet printing process, ink droplets are rapidly absorbed into the coating through capillary action and the image is dry-to-touch right after it comes out of the printer. Although these porous recording elements are relatively fast drying, the resulting dye or pigment deposits that create the image are susceptible to physical damage both during and after printing of the images. This often requires a separate overcoat solution of a durability enhancing polymer or lamination of a polymer sheet over the resulting image in order to achieve acceptable post printing image durability.
Inkjet prints, prepared by printing onto inkjet recording elements, are also subject to environmental degradation. They are especially vulnerable to damage resulting from contact with water and atmospheric gases such as ozone. Ozone bleaches inkjet dyes resulting in loss of density. The damage resulting from the post imaging contact with water can take the form of water spots resulting from deglossing of the top coat, dye smearing due to unwanted dye diffusion, and even gross dissolution of the image recording layer. To overcome these deficiencies, inkjet prints are often laminated. However, lamination is expensive, as a film laminate is a separate roll of material which requires an adhesive layer prepared via an additional coating step. If the laminate is of the transfer type there is also added waste in the form of the exhausted coated support from which the laminate is transferred.
In another approach, fusible thermoplastic polymer particles can be coated as an uppermost porous layer of the recording element. Typically, the thermoplastic polymer particles are coated in a layer several microns thick and ink penetrates through the voids formed between the polymer particles when applied from an inkjet printer. After the ink is applied to the image recording element a fusing step, such as contact with a high temperature fusing roller, is used to heat the polymer particles above their glass transition temperature to form a continuous durable polymer film. This approach has the advantage that the majority of the colored image is covered or entrapped by the fused polymer layer. The resulting image is protected against physical abuse and the fused polymer layer can provide high density to the resulting photographic quality images. Designs for fusible recording elements are disclosed in U.S. Pat. Nos. 4,785,313; 4,832,984; 6,140,390; 6,695,447; 6,777,041; 6,789,891; 6,815,018; 6,866,384; 7,198,363; and 7,264,856.
Image recording elements designed with layers of fusible thermoplastic polymer particles are not without limitations. It is desirable that the fusible polymeric particle layer is of sufficient thickness to accommodate the entire fluid volume of ink that is applied from the printer. Typically, fusible thermoplastic particles have diameters ranging from about 0.1 to about 10 microns. These particle diameters are necessary so that the particles can be completely fused into a continuous layer after printing. In general, the fusible polymer particles are made of materials that are not easily wetted by the inks known in the art of aqueous inkjet printing. In the case of a thick layer of fusible polymer particles there can be adequate capacity to hold the printed ink; however, the ink must be able to penetrate through the voids between the polymer particles instead of coalescing on the surface of the recording element. This is especially problematic when printing pigment-based inks onto the fusible polymer particle layer since the discrete pigment particles can plug the voids between the polymer particles and slow down the flux of ink through the fusible layer.
Fusible particle layers also have the problem of bleeding between inks of different colors into one another which can occur during the printing operation. This is especially true at high ink laydowns where the flux of ink into the porous fusible polymer particle layer is low. It is also desirable that the majority of the ink penetrates through the entire fusible polymer particle layer. This prevents components present in the ink from interfering with the fusing step and allows for high density and high gloss in the imaged areas of the print.
Fusible image recording elements can also show limitations in performance after fusing of the thermoplastic polymer particles. Incomplete fusing of the thermoplastic particles results in weak polymer films that can crack during bending of the recorded image element. Cracking of the polymer film is highly undesirable since the resulting imperfections in the polymer layer can allow destructive chemicals, such as ozone, to chemically attack the colorants, or liquids to stain the printed image. Incomplete fusing of the layer can also result in deglossing artifacts. In some cases, fusible recording elements can show a relatively high gloss immediately after fusing, but lose some amount of gloss over a period of time after fusing. This deglossing artifact can be rationalized as incompletely fused beads that tend to retain their original shape thereby leading to irregularities in the polymer film.
There remains a need to provide image recording elements containing a porous layer of fusible polymer particles that can accept large amounts of ink in a rapid manner without coalescing or bleeding and which show excellent post fusing characteristics such as stain resistance, deglossing resistance and crack resistance that provide high quality durable photographic images.